calibrating a laser level

I have recently bought a laser level but it doesn't come with a manual.
I'm having a few troubles sometimes calibrating the thing as there are three water levels to be set: one for the tripod, another for the base and the third for the level itself. The level on the base is particularly tricky because the base itself has to be rotated (useful feature for many jobs). Has anyone found a trusted and quick way of calibrating optical instruments using three adjustable screws?
Any hint would be appreciated.
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Standard technique as for levelling a surveyor's theodolite. (They tend to have straight vials, rather than bulls-eye bubbles.)
Assuming you've got the same kit as me! Stand opposite the "0" degree mark. Choose the two screws close to you (at the 60 & 300 deg. marks). You now level in a sideways mode using these two screws together but turning equally in opposite directions until the bubble is centred side to side; and then using the third screw on the far side (180 deg) you bring the bubble into the centre of the circle. Check by rotating the head through 180 deg adjusting if necessary, and then by carefully rotating the head and watching what happens to the bubble. If there are errors, try to take out just half the error, rotate and take out half the error; etc.......
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M Stewart
Milton Keynes, UK
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